Malaria, a disease transmitted by mosquitoes, continues to be a significant global public health issue. It causes the deaths of millions of people annually, primarily in tropical countries of Africa and South Asia (Sato, 2021). The report of World Health Organization (WHO) 2021 states that there were 619,000 deaths from malaria worldwide out of a total of 247 million cases worldwide (WHO, 2022). Due to its low efficacy, the WHO did not endorse the falciparum malaria vaccine, which was developed in 2015 (Draper et al., 2018). Current antimalarial drugs are gradually developing resistance and losing their effectiveness in preventing and treating malaria infection. Chloroquine (CQ) has been a popular drug since 1940s and provides numerous benefits such as excellent efficacy, minimal danger of adverse reactions, and affordability (Titus, 1989). The emergence of drug resistance to antimalarial medications including chloroquine, amodioquine, artemisinin, and antifolates is a growing health issue (Shibeshi et al., 2020), thus, the Southeast Asia and South America have switched from chloroquine (CQ) to artemisinin-based combination therapy (ACT) (Eastman and Fidock, 2009). However, emerging drug resistance to these medications prompts researchers to find alternative antimalarial treatments. A malaria research study has identified P. falciparum dihydrofolate reductase (Pf-DHFR) as clinically recognized targets, which is inhibited by cycloguanil, chlorcycloguanil and WR99210 (Yuthavong et al., 2012). The bifunctional enzyme dihydrofolate reductase-thymidylate synthase of Plasmodium falciparum (Pf-DHFR-TS) was studied structurally and mutagenically to identify important properties for effective DHFR inhibitors. According to Cowman and Yuthavong, hydrogen bonding occurred solely with the amino acid chain containing carboxyl oxygen of ILE A: 14, ASP A:54 and ILE A: 164. It has been reported that 1,3,5-triazine scaffold created H-bonds with ILE A:14, LEU A:46, ASP A:54 and ILE A:164 involving nitrogen atom (Cowman et al., 1988; Yuthavong et al., 2005). Moreover, in our previous study, we have showed the significance of H-bonds, and found that 1,3,5-triazine created numerous H-bond with ASP A:54, MET A:55, SER A:111, ARG A:122, ILE A:164 and TYR A:170 located within the active sites of Pf-DHFR-TS (Gogoi et al., 2021). Various 1,3,5-triazine compounds have been shown to be effectively inhibit DHFR against malaria (Adhikari et al., 2020), and also has various pharmacological activity such as antibacterial (Ma et al., 2011), A2A antagonist (Masih et al., 2020), antifungal (Singh et al., 2012), anticancer (Srivastava et al., 2017), towards cystic-fibrosis (Srivastava et al., 2015) and antivirals (Sakakibara et al., 2015).

Pyrazole is another pharmacophore that contains doubly unsaturated five-membered heterocyclic compounds with two nitrogen atoms (Brullo et al., 2020), which is a very important structure in medicinal chemistry showing diverse biological activities (Costa et al., 2021). Our group's recent papers reported the synthesis and evaluation of PABA-substituted 1,3,5-triazine compounds (I), which exhibited good activity against the CQ-sensitive 3D7 strain with an IC50 of 39.50 μg/mL (Saha et al., 2023). Further, trimethoxy phenyl substituted pyrazole-1,3,5-triazine hybrid molecule (II) exhibited significant activity against the CQ-sensitive 3D7 strain with an IC50 of 25.02 μg/mL (Borgohain et al., 2024). The in vitro antimalarial assay results indicated that 4-aminobenzoyl-l-glutamic acid substituted 1,3,5-triazine hybrid derivatives (III) (Adhikari et al., 2022) had superior antimalarial activity against chloroquine-sensitive (3D7) and chloroquine-resistant (Dd2) strains shown in Fig. 1. The current study aims to prepare ten compounds that contain two pharmacophores, including pyrazole and 1,3,5-triazine. These compounds were synthesized using conventional methods and tested for antimalarial activity against chloroquine-sensitive (3D7) and resistant (Dd2) strains of P. falciparum.